This project intends to study the effects of micrometeorologic conditions on the development of the eggs and larvae of the gastrointestinal nematodes of sheep, Haemonchus contortus, Cooperia spp., Ostertagia circumcincta, Bunostomum trigonocephalum. Trichostrongylus axei and other nematodes of domestic animals such as Ancylostoma caninum, and also of the survival of these stages on pasture and outside the host animal. Maximum, minimum and mean temperatures will be measured at the soil surface and in a standard weather shelter; precipitation, soil moisture, relative humidity and other micrometeorologic factors will also be measured; and these will be correlated by means of the IBM 360 computer with the development and survival of the free-living nematode stages. The effects of pasture conditions on the parasitic stages will also be determined. The effects of the measured factors and of repeated desiccation will also be studied under controlled conditions in the laboratory, and the roles of possible invertebrate transport hosts (if any) will be determined. Comparisons will be made with information already gained in similar studies on Haemonchus contortus and Trichostrongylus colubriformis. This work will be used as a mode for epidemiologic studies of other diseases and disease agents of man and other animals.